- buildAxis: IP1 → IP4 → IP3 as stretches with their own frames; arc length s
from IP1; mitre normal u1 + u2 at the kink.
- toAxis / fromAxis: world ↔ (k, s, n) round trip; stretch chosen by the mitre plane.
- copingSpan (centred on L_IP/2) and nearKink (columns within the Level half-width).
- Straight P1 regression against spec §12 bearing values; bent round trip and continuity.
- Not wired into buildPier yet; the model still refuses bent coping (미실시).
Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>
